Douglas Vincent Mastriano (born January 2, 1964) is an American far-right politician and retired military officer who has served in the Pennsylvania Senate since 2019, representing the 33rd district. A member of the Republican Party, he was also the party's nominee in the 2022 Pennsylvania gubernatorial election.

Born in New Jersey, Mastriano served in the United States Army from 1986 to 2017 and attained the rank of colonel. He ran for U.S. Congress in Pennsylvania's 13th congressional district in 2018, where he finished fourth in the primary. Mastriano won the state senate seat for the 33rd District the following year in a special election. In 2022, he won the Republican nomination for governor and lost to Democratic state attorney general Josh Shapiro in the general election.

Mastriano is a prominent figure in fundamentalist Christian nationalism and has called the separation of church and state a myth. He has made social media posts referencing QAnon and has spoken at events that promoted QAnon and 9/11 conspiracy theories. An election denier and self-professed close ally of former president Donald Trump, Mastriano received national attention for his efforts to overturn the 2020 United States presidential election.

He attended Trump's January 6 rally in Washington, D.C., prior to Trump supporters' storming of the United States Capitol, and was seen on video passing through Capitol Police barriers after they had been breached by others in the crowd. Mastriano was subpoenaed by the United States House Select Committee on the January 6 Attack in February 2022, but stopped cooperating with the Select Committee the following August.